1. Field of the Invention
The present invention relates to a groove machining method for forming thin bottomed grooves in the surface of a metal workpiece using a laser and a honeycomb structure forming die using the same method and a method for producing the same die.
2. Description of the Related Art
Conventionally, machining using a laser has been used for welding and cutting a workpiece, but there has been no case where the laser machining is used for machining grooves having bottoms or bottomed grooves. In a cutting method using laser, a laser beam is emitted onto the workpiece to melt it, and a melted portion is removed with an assist gas or high-pressure water. To be specific, a laser beam is emitted onto the workpiece in such a manner as to be converged to a single location thereon so as to form a through hole, and then the laser beam emitting location is shifted to form another through hole in the workpiece. Thus, the workpiece is cut by continuously forming through holes.
In a case where an attempt is made to use this method to form grooves, it is possible to form through grooves which have no bottoms, but bottomed grooves have not been formed using the method. In addition, in the method in which the melted portion is removed by jetting high-pressure water, water remains on the surface of the workpiece, causing a problem that the path along which the laser beam is emitted is altered owing to the water so remaining on the surface of the workpiece, whereby the laser beam cannot be emitted onto a desired position with accuracy.
On the other hand, grid-like grooves are formed in a honeycomb structure forming die from which a ceramic honeycomb form is extruded. Most of these grooves are bottomed grooves which are large in depth and small in width. While grinding or electrical discharge machining has been used a method for forming such grid-like grooves, as there is an increasing tendency that the widths of grooves are required to be narrower to such as 100 μm or smaller, it is becoming more difficult to employ the aforesaid grinding and electrical discharge machining in which a grinding wheel and electrodes are physically used, respectively.
Incidentally, for example, a ceramic honeycomb structure made from mainly cordierite is produced by extruding the material using a forming die. This honeycomb structure so formed is constituted by many cells which are formed by providing bulkheads in a grid-like fashion, and in many cases the cells are each formed into, for example, a quadrilateral or hexagonal shape.
In addition, the aforesaid honeycomb structure forming die is used as a honeycomb structure forming die having supply holes for supplying a material and grooves adapted to communicate with the supply holes, respectively, for forming the material supplied from the supply holes into the aforesaid honeycomb shape.
In recent years, there has been a demand that the thickness of bulkheads of the honeycomb structure is smaller and is, for example, 100 μm or smaller. To cope with this demand, naturally, the width of the grooves of the honeycomb structure forming die must also be smaller.
However, if the width of the grooves of the honeycomb structure forming die is made narrower, as required, the flowability of the material which is supplied from the supply holes and then passes through the grooves is deteriorated. This increases the forming pressure while forming is carried out, leading to a risk that formability is reduced.